Defect and Dopant Properties of the SrCeO₃-Based Proton Conductor

Abstract

Atomic-scale studies using advanced simulation techniques have investigated the energetics of defects, oxygen migration, and dopant incorporation in the proton-conducting SrCeO3 system. The interatomic potential model first reproduces the observed distorted perovskite structure of SrCeO3. Substitution with trivalent dopants (M) on the A site in SrCe(Yb)O3-δ (via Vo•• consumption) is compared with substitution on the B site (via Vo•• creation); the results support the premise that the absence of ionic conductivity at low doping levels is associated with dopant partitioning over both A and B sites. Dopant-vacancy association is predicted to occur in SrCe0.9M0.1O2.95 for a wide range of M cations. Formation of (M‘Ce−OHo•) clusters is also calculated to be favorable in accordance with reported proton-trapping effects. The lowest M‘Ce−OHo• binding energies and the largest M−H distances are found for the most common dopants for proton conductivity in the SrCeO3 system, namely, Y and Yb. The pathway for oxygen migration is proposed as a curved trajectory with an asymmetric energy distribution. The lowest energy redox process is calculated to be oxidation with the formation of holes in accordance with the observation of p-type conductivity at increasing oxygen partial pressures (pO2).